1. Field of the Invention
This invention relates to single mode optical fibers and more particularly to such optical fibers having reduced loss resulting from small radius bends.
2. Description of the Prior Art
Single mode optical fibers have been designed for and used in the telecommunication industry since about 1980. Single mode optical fibers can offer low attenuation and low dispersion at each of the typical operating wavelengths, namely, 1.3 um and 1.55 um. The bend induced attenuation performance of such designs was compromised to provide for optimal use in a variety of cable structures intended primarily for linear deployment.
It has been observed, however, that if such fibers are subjected to a few bends of small radius, dramatic attentuation increases occur. Similarly, if such fibers are wound under tension on cylinders or bobbins, they exhibit large changes of attenuation with temperature variation. The bend performance of these telephony designs has been compromised to achieve the lowest attenuation at the desired operating wavelengths consistent with low splice loss for linear deployment. Thus, the bend performance of these single mode optical fibers has been sacrificed to provide a structure that may be spliced without experiencing significantly increased splice losses. The mode field diameters of the typical single mode optical fibers used in telecommunications, is in the range of 7.5 to 11.0 um.
A single mode optical fiber has not been made available for use in guidance applications wherein an optical fiber extends from a control station to a moving vehicle and wherein the optical fiber is stored on a cylinder or bobbin and is payed out as the vehicle moves away from the control station.